Just How Fast is Light, Anyway?

In Light Travels About*
1 second 186,000 miles = 300,000 kilometers
1 millisecond 186 miles = 300 kilometers
1microsecond 1000 feet = 300 meters
1 nanosecond 1 foot = 30 centimeters
1 picosecond 12 mils = 300 microns

*In free space; in a wire and especially in coaxial cable, the speed of signals can be much slower. Common coax cables have "velocity factors" from 0.85 to 0.66 -- meaning that electricity (which in free space moves at the same speed as light) travels only 85 to 66 percent as fast through those cables.